1. Field of the Invention
The present invention relates to a production method of an optical film, an optical film and an image display.
2. Description of Related Art
In various image displays such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), cathode ray tube display (CRT), field emission display (FED) and surface-conduction electron-emitter display (SED), an antireflection film is disposed on the display surface so as to prevent reduction in the contrast due to reflection of outside light or reflection of an image. Accordingly, the antireflection film is required to have high transmittance, high physical strength (e.g., scratch resistance), chemical resistance and weather resistance (e.g., humidity/heat resistance, light fastness) in addition to high antireflection performance.
For the formation of an antireflection layer (e.g., high refractive index layer, medium refractive index layer, low refractive index layer) used in the antireflection film, a method of coating a coating composition (wet coating) has been proposed.
In producing the antireflection film by a coating method, a single-layer or multilayer thin film needs to be formed by dissolving or dispersing a film-forming composition having a specific refractive index in a solvent, coating the prepared coating composition on a transparent support substrate, and drying and if desired, curing the coating. In the case of a single-layer film, a layer (low refractive index layer) having a refractive index lower than that of the substrate may be formed to a thickness of, in terms of the optical film thickness, ¼ the wavelength designed. When more reduction of reflectance is necessary, this may be attained by forming a layer (high refractive index layer) having a refractive index higher than that of the transparent support between the substrate and the layer having a low refractive index. In order to still more reduce the reflectance, an embodiment where a medium refractive index having a refractive index between the transparent support and the high refractive index layer is provided on the transparent substrate side of the high refractive index layer has been also proposed (see, JP-A-2003-121606).
In the case of forming a plurality of layers differing in the refractive index, the number of coating steps increases and this brings about a problem such as bad productivity and cost rise or a problem that when the adhesion between two layers is low, the scratch resistance is worsened. In order to solve these problems, a technique of simultaneously forming two different layers has been proposed (see, JP-A-2004-317734 and JP-A-2004-359930). For example, a production method of an antireflection film, where a coating solution containing both a fluorine-containing polymer and an inorganic fine particle is coated and cured one time, thereby simultaneously forming a high refractive index layer containing an inorganic fine particle and a low refractive index layer containing a fluorine-containing polymer, has been disclosed (see, JP-A-2004-317734). That is, two coating layers are formed by one-time single-layer coating. However, as regards the production method of an optical film, a technique capable of achieving low reflectance, neutral tint, high scratch resistance, high productivity, good surface state and the like has not yet been specifically proposed, and improvement of these properties is demanded.